1. Field
One embodiment of the present invention relates to a disk drive in which power is supplied to the heating element provided on the head, thereby changing the thermal expansion of the head to adjust the dynamic fly height of the head, and also to a method of adjusting the dynamic fly height of the head. More particularly, the invention relates to a disk drive in which the dynamic fly height of the head is well adjusted when the head undergoes an abnormal movement, and to a method of adjusting the dynamic fly height of the head in such an event.
2. Description of the Related Art
Hard disk drives (HDDs) are well known as representative examples of disk drives in which disks are used as recording media. Each HDD has a head (magnetic head) that is configured to write data in, and read data from, the disk (magnetic disk). The head flies above the disk as the disk is rotated.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2007-042239 (hereinafter referred to as Prior Art Document 1) discloses an HDD in which a heating element (heater) is provided on the head (head slider). In the HDD disclosed in Prior Art Reference 1, the power supplied to the heating element is controlled, changing the thermal expansion (deformed amount) of the head. The distance between the head and the disk (more precisely, the surface of the disk), i.e., so-called dynamic fly height, is thereby adjusted. The heating element is called DFH heater, and the power supplied to the heating element is called DFH power.
For example, PCT International Publication No. 2002/037480 (hereinafter referred to as Prior Art Document 2 describes a technique of changing the voltage applied or current supplied to an electrically conductive film that is equivalent to the above-mentioned heating element, thereby adjusting the temperature of the head in order to adjust the thermal expansion of the head. Prior Art Document 2 also describes a technique of controlling the voltage applied or current supplied to the electrically conductive film (for example, not applying the voltage or supplying the current to the film), thereby to reduce the thermal expansion of the head while the head is being loaded or unloaded. The techniques disclosed in Prior Art Document 2 can prevent the head from colliding with the tiny projections existing on the disk surface, while the head is being loaded or unloaded.
The HDDs developed in recent years can record data in the disk at high density. The higher the recording density, the more the dynamic fly height of the head should be reduced. It is therefore important to use the techniques described in Prior Art Documents 1 and 2, thereby to adjust the dynamic fly height of the head. However, if the dynamic fly height of the head is small, or while the DFH power is being supplied to the heating element (hereinafter referred to as DFH-power ON state), a phenomenon may develop. That is, the head flies unstably in the DFH-power ON state, and will probably collide with the magnetic disk, causing a so-called head clash.
Assume that the head is moved to a target track on the disk and that a head positioning control (i.e., track following control) is then performed, thus positioning the head at a target position on the target track. If a small dynamic fly height is set for the head in the DFH-power ON state, the head may collide with the tiny projections existing on the disk surface. If the head collides with these projections, it will temporarily move in an unintended direction. If the head so moves, it will fly in an unstable manner. If the head flies unstably with its dynamic fly height set to a small value, a head clash will probably occur.